CVE-2025-27740: Windows Server 2008 Privilege Escalation

CVE-2025-27740 Overview

CVE-2025-27740 is a privilege escalation vulnerability affecting Windows Active Directory Certificate Services (AD CS). The vulnerability stems from weak authentication mechanisms that allow an authorized attacker with low-level access to elevate their privileges over a network. This flaw in AD CS represents a significant security concern for enterprise environments relying on Microsoft's certificate infrastructure for identity management and secure communications.

Active Directory Certificate Services is a critical Windows Server role that provides customizable services for issuing and managing public key infrastructure (PKI) certificates. A weakness in the authentication process could enable attackers to obtain certificates they are not authorized to receive, potentially leading to domain privilege escalation, impersonation attacks, or unauthorized access to sensitive resources.

Critical Impact

An authorized attacker can leverage weak authentication in AD CS to escalate privileges over the network, potentially gaining administrative control over domain resources and compromising organizational security.

Affected Products

• Microsoft Windows Server 2008 SP2 (x86 and x64)
• Microsoft Windows Server 2008 R2 SP1 (x64)
• Microsoft Windows Server 2012
• Microsoft Windows Server 2012 R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022
• Microsoft Windows Server 2022 23H2
• Microsoft Windows Server 2025

Discovery Timeline

• 2025-04-08 - CVE-2025-27740 published to NVD
• 2025-07-10 - Last updated in NVD database

Technical Details for CVE-2025-27740

Vulnerability Analysis

This vulnerability is classified under CWE-1390 (Weak Authentication), indicating that the authentication mechanisms implemented in Windows Active Directory Certificate Services fail to adequately verify the identity or authorization level of requesting entities. The flaw allows an attacker who already has some level of authenticated access to the network to request and obtain certificates beyond their authorized scope.

AD CS vulnerabilities have historically been high-value targets for attackers due to the central role certificate services play in enterprise security. Certificate-based attacks can enable persistent access, lateral movement, and privilege escalation within Active Directory environments. The network-based attack vector with low complexity requirements makes this vulnerability particularly concerning for organizations with exposed certificate enrollment endpoints.

Root Cause

The root cause of CVE-2025-27740 lies in insufficient authentication validation within the Active Directory Certificate Services component. The weak authentication implementation fails to properly verify that requesting users have appropriate authorization levels before processing certificate enrollment requests. This authentication gap allows users with limited privileges to obtain certificates that grant elevated access rights.

Attack Vector

The attack is conducted over the network and requires the attacker to have valid credentials with low-level privileges on the target system. No user interaction is required to exploit this vulnerability. An attacker would typically:

1. Authenticate to the domain with low-privileged credentials
2. Identify vulnerable AD CS enrollment endpoints
3. Submit crafted certificate enrollment requests that exploit the weak authentication
4. Obtain certificates with elevated privileges
5. Use the obtained certificates to authenticate as a higher-privileged user or service

The vulnerability does not require complex attack chains or specialized tools, making it accessible to attackers with basic knowledge of AD CS certificate enrollment processes. Successful exploitation can result in complete compromise of confidentiality, integrity, and availability of affected systems.

Detection Methods for CVE-2025-27740

Indicators of Compromise

• Unusual certificate enrollment requests from low-privileged user accounts
• Certificate requests for high-privilege templates from unexpected sources
• Anomalous authentication events using newly issued certificates
• Unexpected changes in certificate enrollment logs on AD CS servers

Detection Strategies

• Monitor Windows Security Event Logs for Event ID 4886 (Certificate Services received a certificate request) from unexpected accounts
• Audit AD CS certificate templates for enrollment permissions that may allow unauthorized access
• Review Event ID 4887 (Certificate Services approved a certificate request) for certificates issued to suspicious principals
• Implement certificate request filtering and alerting based on user privilege levels

Monitoring Recommendations

• Enable verbose logging on all AD CS servers and centralize log collection
• Configure alerts for certificate enrollment requests from service accounts or low-privileged users requesting high-privilege templates
• Regularly audit certificate template permissions and enrollment agent configurations
• Monitor for use of newly issued certificates in authentication events across the domain

How to Mitigate CVE-2025-27740

Immediate Actions Required

• Apply the latest Microsoft security updates addressing CVE-2025-27740 to all affected Windows Server systems
• Audit AD CS certificate template permissions and restrict enrollment rights to authorized users only
• Review and restrict certificate enrollment endpoints to minimize network exposure
• Enable Manager Approval for sensitive certificate templates to add manual verification

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should consult the Microsoft Security Update Guide for CVE-2025-27740 for detailed patch information and download links specific to their Windows Server versions. Apply patches to all AD CS servers as a priority, followed by domain controllers and member servers.

Workarounds

• Restrict network access to AD CS enrollment endpoints using firewall rules or network segmentation
• Remove enrollment permissions from Built-in Users and other broad security groups on certificate templates
• Implement certificate template restrictions requiring specific security group membership for enrollment
• Enable "CA Certificate Manager Approval" on sensitive templates to require manual approval of certificate requests

# PowerShell: Audit certificate template permissions
# Run on AD CS server to identify templates with broad enrollment rights
Import-Module ADCSAdministration
Get-CATemplate | ForEach-Object {
    $template = $_
    Get-CATemplate -Name $template.Name | 
    Select-Object Name, @{N='EnrollmentPermissions';E={$_.EnrollmentPermissions}}
}

# Review certificate enrollment logs
Get-WinEvent -FilterHashtable @{
    LogName='Security'
    ID=4886,4887
} -MaxEvents 100 | Format-Table TimeCreated, Message -AutoSize